Onlookers watched as girls as young as 13 and 14 allegedly took part in a brutal and prolonged assault where a man was stripped and degraded in Hamilton.
Police said the assault was carried out during a small social gathering at an inner city apartment in the early hours of Saturday morning.
The victim was with the alleged offenders - four of whom were girls - when they turned on him and held him captive for more than an hour, police said.
Detective sergeant Ricky Thompson said the offenders removed the man's clothing and put it in his mouth as a gag while others at the gathering looked on.
The man was repeatedly beaten, abused and degraded, Mr Thompson said. Parts of his hair were cut before he managed to make his escape.
"This was a prolonged, serious and humiliating assault for the victim."
Mr Thompson said no charges could be laid against the people who looked on as the assault was carried out.
It was concerning that four of the five who allegedly carried out the attack were female and that one was as young as 13, he said.
"This was a seriously violent incident with these young girls being involved in an offender role."
"It's a concern to anyone that young people are involved in such crimes. And that it's young women is concerning - I think everyone would agree on that."
The victim suffered a fractured cheek and severe bruising in the attack. He has been discharged from hospital and is recovering at home.
Five people have appeared in the Hamilton Youth Court to face charges of grievous bodily harm, assault with a weapon, threatening to kill and theft over the incident.
Three were given bail, one remains in custody and one was still in court his afternoon, Mr Thompson said.
Recent legislation changes makes it possible to lay charges when youths are involved in violent crimes, he said.
Violent incidents involving teenage girls have been on the rise in New Zealand.
In 2009, Statistics NZ recorded 1501 teenage girls aged 14-16 being apprehended for violent crimes, including assaults, intimidation and threats.
That compared to 1402 in 2008 and 1205 in 2007.
In a June assault, a drunk teenage girl allegedly hit a 73-year-old Panmure dairy owner in the head with a hammer to steal chocolate bars and cigarettes.
Three girls and a boy, all aged 14, and a 15-year-old girl appeared in the Youth Court
charged with aggravated robbery over the incident.
Horrific cellphone footage released in March captured a savage attack on 15-year-old Wanganui Girls' College student Robin de Jong by another teenage girl.